What's the valve cover in an engine?

Rocker covers are covers that are bolted on over rocker arms in an internal combustion engine. They are called valve covers in the United States, Canada, and in situations where Rocker Arms are not present, such as some Overhead Cam, and most Dual Overhead Cam engines. and rocker boxes in the United Kingdom.

On modern engines without rocker arms they are internationally known as "valve cover" but are sometimes refereed to as a "cam cover" or "timing cover" if they also cover the timing gear(s) and belt or chain.

V engines (V6, V8, etc.) usually have two rocker covers, one for each bank of cylinders, while straight engines (I4, I6, etc.) and single-cylinder engines usually have one rocker cover. Very large multi-cylinder engines, such as those used in a ship or in aviation, may have one rocker cover for each cylinder, to make removal and installation more manageable.

Valve cover in the engine is nothing but the cover mounted over the inlet and exhaust valves of the engine to protect the valves. 

Valve cover is only a protection cover of valves ,also normally called as tappet cover in India.If any one want to adjust the clearance of valves,He have to open the valve cover and then set the clearance.

The valve cover is a metal cover that is found on very top of the engine. The valve cover is attached to the engine by a gasket made of rubber or cork. The valve cover and gasket seal the top of the engine and preventOIL leaks. These covers are removable so the mechanic can access the valves for adjustment. Because of the high temperature of the engine, it is common for the valve cover gasket to get brittle and break. If the gasket is worn out, it will leak engine oil and the top of the engine will be covered in oil. Since the engine is losing oil, running the car for too long without an inspection and repair can cause engine damage.

I agree with the expert answers.